1. Field of the Invention
The invention relates to an ink jet apparatus.
2. Description of Related Art
As a printer head, there has conventionally been proposed a drop-on-demand type of ink jet printer head using piezoelectric ceramics. In this type of ink jet printer head, the volume of an ink chamber is changed by deforming the piezoelectric ceramics. When the volume is decreased, ink contained in the ink chamber is expelled in the form of droplets from a nozzle, whereas when the volume is increased, additional ink is introduced from an ink supply passage into the ink chamber. A plurality of such nozzles are arranged in neighboring relationship to each other, and the ink droplets are expelled from desired ones of the nozzles according to desired print data to thereby form desired characters or images on a sheet of paper or the like opposed to the nozzles.
This kind of ink jet apparatus is disclosed in U.S. Pat. Nos. 4,879,568; 4,887,100; 4,992,808; and 5,003,679; U.S. Pat. No. 5,028,936 (corresponding to Japanese Patent Laid-open Nos. Sho 63-247051 and 63-252750); and U.S. Pat. No. 5,016,028 (corresponding to Japanese Patent Laid-open No. Hei 2-150355), for example. FIGS. 15 to 19 schematically show such a conventional ink jet apparatus.
The structure of such a conventional ink jet apparatus will now be described with reference to FIG. 15 which shows a cross section thereof. Reference numeral 1 denotes a piezoelectric ceramics plate having a plurality of grooves 15 and side walls 11 partitioning these grooves 15 and polarized in a direction depicted by an arrow 4. Reference numeral 2 denotes a cover plate formed of a one of several materials, such as ceramics and resins. The piezoelectric ceramics plate 1 and the cover plate 2 are bonded together by an adhesive layer 3 formed of an epoxy adhesive, for example, whereby the plural grooves 15 are formed as a plurality of ink chambers 12 spaced from each other in a transverse direction of the piezoelectric ceramics plate 1. Each ink chamber 12 is rectangular in cross section and is elongated over the length of the piezoelectric ceramics plate 1. Each side wall 11 extends over the length of the ink chamber 12 it defines. The adhesive layer 3 is formed on the upper surface of each side wall 11. A pair of metal electrodes 13, for applying a driving electric field, are formed on the opposed side surfaces of each ink chamber 12 at an upper half portion thereof. All of the ink chambers 12 are filled with ink.
The operation of the ink jet apparatus shown in FIG. 15 will now be described with reference to FIG. 16 showing a cross section thereof. When the ink chamber 12b, as an exemplary one of the ink chambers 12, is selected according to desired print data, a positive driving voltage is rapidly applied to the metal electrodes 13e and 13f, formed on the inside of the ink chamber 12b, and the metal electrodes 13d and 13g formed on the outside of the ink chamber 12b are grounded. As a result, a driving electric field having a direction 14b is generated in the side wall 11b, and a driving electric field having a direction 14c is generated in the side wall 11c. As the directions 14b and 14c of the driving electric fields are perpendicular to the direction 4 of polarization of the piezoelectric ceramics plate 1, the side walls 11b and 11c are rapidly deformed inwardly of the ink chamber 12b by a piezoelectric thickness shear effect. This deformation of the side walls 11b and 11c reduces the volume of the ink chamber 12b to rapidly increase the pressure of the ink contained in the groove 12b and thereby generate a pressure wave. As a result, the ink droplets are expelled from a nozzle 32 (see FIG. 17) communicating with the ink chamber 12b. Further, when the application of the driving voltage is gradually stopped, the side walls 11b and 11c gradually restore their original positions before deformation (see FIG. 15), and the pressure of the ink contained in the ink chamber 12b is therefore gradually decreased. As a result, additional ink is supplied from an ink inlet hole 21 through a manifold 22 (see FIG. 17) into the ink chamber 12b.
The above operation is merely a basic operation of the ink jet apparatus in the prior art. In an actual product, however, a driving voltage may be first applied in a such a direction as to increase the volume of the ink chamber 12b to supply the ink into the ink chamber 12b before expelling the ink, and thereafter the application of the driving voltage may be rapidly stopped to return the side walls 11b and 11c to the original positions and thereby expel the ink.
The structure and a manufacturing method for the ink jet apparatus shown in FIG. 15 will now be described with reference to FIG. 17 showing a perspective view thereof. The parallel grooves 15 forming the ink chambers 12 are formed in the piezoelectric ceramics plate 1 by cutting with use of a thin, disk-shaped diamond blade. All the grooves 15 are parallel and have the same depth over almost the entire length of the piezoelectric ceramics plate 1. The depth of each groove 15 is gradually reduced as it approaches a rear end surface 17 of the piezoelectric ceramics plate 1 to form a shallow groove 18 near the rear end surface 17. Thereafter, the metal electrodes 13 are formed on the inner surfaces of the grooves 15 and the shallow grooves 18 by a known technique such as sputtering. More specifically, the metal electrodes 13 are formed on the upper half portions of the inner side surfaces of the grooves 15 and also on the inner side and bottom surfaces of the shallow grooves 18. On the other hand, the ink inlet hole 21 and the manifold 22 are formed in the cover plate 2 by a method such as grinding or cutting.
Then, the lower surface of the cover plate 2, in which the manifold 22 is formed, is bonded to the upper surface of the piezoelectric ceramics plate 1, in which the grooves 15 are formed, by means of an epoxy adhesive or the like, thereby defining the ink chambers 12 from the grooves 15. Then, a nozzle plate 31, having the nozzles 32 arranged at the positions corresponding to the front end positions of the ink chambers 12, is bonded to the front end surface of the assembly of the piezoelectric ceramics plate 1 and the cover plate 2. A substrate 41, having a plurality of conductor film patterns 42 arranged at the positions corresponding to the rear end positions of the ink chambers 12, is bonded to the lower surface of the piezoelectric ceramics plate 1, on the opposite side from the cover plate 2, by means of an epoxy adhesive or the like. Then, each conductor film pattern 42 is connected by wire bonding through a conductor wire 43 to the metal electrode 13 which is also formed on the bottom surface of the shallow groove 18 contiguous to the corresponding groove 15.
The structure of a control section for controlling the ink jet apparatus shown in FIG. 17 will be described with reference to FIG. 18 which shows a block diagram of the control section. The conductor film patterns 42 formed on the substrate 41 are individually connected to an LSI chip 51. Also connected to the LSI chip 51 are a clock line 52, a data line 53, a voltage line 54, and a ground line 55. The LSI chip 51 determines which nozzle 32 the ink droplets are to be expelled from according to data appearing on the data line 53 on the basis of continuous clock pulses supplied from the clock line 52. Then, according to the result of the determination, the LSI chip 51 applies a voltage V from the voltage line 54 to the conductor film pattern 42 connected to the metal electrode 13 in the ink chamber 12 to be driven. Further, the LSI chip 51 applies the zero voltage of the ground line 55 to the other conductor film patterns 42 connected to the metal electrodes 13 in the ink chambers 12 that are not to be driven.
Next, a printer employing the ink jet apparatus of the prior art will be described with reference to FIG. 19, showing a perspective view of the printer. The printer shown in FIG. 19 includes an ink jet apparatus 61 and a nozzle plate 31 similar in constitution and operation to those shown in FIGS. 15 to 17.
The ink jet apparatus 61 is fixed to a carriage 62. An ink supply tube 63 is connected to the ink inlet hole 21 (see FIG. 17). The LSI chip 51 (see FIG. 18) is installed in the carriage 62. A flexible cable 64 corresponds to the clock line 52, the data line 53, the voltage line 54, and the ground line 55 shown in FIG. 18. The carriage 62 is reciprocated along a slider 66 in opposite directions depicted by a double-headed arrow 65, over the width of a recording paper 71. During movement of the carriage 62, the ink jet apparatus 61 operates to jet ink droplets from nozzles 32 (see FIG. 17) of the nozzle plate 31 onto the recording paper 71 supported on a platen roller 72, thereby depositing the ink droplets on the recording paper 71. When the ink jet apparatus 61 jets the ink droplets, the recording paper 71 is kept at rest. Every time the carriage 62 changes the direction of reciprocation, the recording paper 71 is fed by paper feed rollers 73,74 by a given amount in a direction depicted by arrow 75 in FIG. 19. Accordingly, the ink jet apparatus 61 can form desired characters or images on the whole surface of the recording paper 71.
In the conventional ink jet apparatus 61 described above, however, the pressure wave generated in the ink contained in the ink chamber 12 scans toward the corresponding nozzle 32 to jet the ink droplets from the nozzle 32. Accordingly, the number of energy generating means including the side walls 11, the metal electrodes 13, and the number of the ink chambers 12 must be equal to the number of the nozzles 32. As a result, the structure of the apparatus 61 becomes complicated and a driving circuit for driving the energy generating means becomes complicated and enlarged in size. Accordingly, the ink jet apparatus 61 increases in cost and size as a whole.
Further, in forming a so-called line head such that the nozzles 32 of the ink jet apparatus 61 are arranged with the same integration degree as that desired to deposit the ink droplets on the recording paper 71 and arranged over the width of the recording paper 71, the numbers of the energy generating means and the ink chambers 12 are greatly increased to cause a great increase in cost and size of the ink jet apparatus 61 as a whole.